In a known device of this kind (U.S. Pat. No. 3,058,687) there are arranged, on a flange that is secured to the winding shaft and on the inertia blocking wheel, respectively, three oblique saw-tooth-form cam and cam engaging surfaces. In the release condition, the three "saw teeth" consistently grip into one another, whereby the steep tooth flanks provide striking surfaces which prevent a further movement of the inertia blocking wheel under the action of the release spring. The movement of the inertia blocking wheel in the blocking condition takes place in the direction towards the free end of the winding shaft. The counter-blocking elements are formed on a cover that closes the housing, which, for this purpose, must be maintained strong and rigid. When a device of this type is installed in a vibrating vehicle, particularly a moving power vehicle, a noise formation usually cannot be avoided. The weak release spring of course presses the inertia blocking wheel with only a very small force in the withdrawal condition, so that the steep tooth flanks, through vibration and jerky tension changes in the web, repeatedly become temporarily disengaged and thereafter strike one another again. The metal tooth flanks thereby produce a rattling and annoying noise. The necessity for applying a stiff, strong cover for closing the housing, moreover, makes the construction heavy and also somewhat expensive.
To avoid the last mentioned disadvantages, it is known to move the inertia blocking wheel in the direction away from the free end of the winding shaft in the blocking condition. The counter-blocking elements can then be formed on a partition in the housing that must nonetheless be substantially strong in order to accommodate a bearing for the winding shaft. With this, provision must be made for having the inertia blocking wheel, in the release condition, lie against a stop that prevents its sliding off of the free end of the winding shaft. For this there can usually be employed a spring ring mounted on the winding shaft. Here, too, unpleasant chattering noises arise in the release condition through the contact of two metal surfaces. In addition, with this known arrangement there is provided, for the axial movement of the inertia blocking wheel, a threaded engagement between this wheel and the winding shaft which demands an expensive and very precise thread cutting.